We are facing major                                      

Problems it is reported that                                 

                                            .

   There are two basic sources of these problems. One is man-made, for example,                                             

                       . The other is a natural catastrophe.

                                       .

  Then, how should we                                    

                              ? One method is             

                     Or perhaps                         

                    is a better way to                     

                  In addition,                            

                                                .

1、提出问题

2、问题来源之一

3、问题来源之二

4、解决方法之一

5、解决方法之二

6、解决方法之三